Nature and Light Dependence of Bulk Recombination in Co-Pi-Catalyzed BiVO 4 Photoanodes

BiVO 4 is considered to be a promising photoanode material for solar water splitting applications. Its performance is limited by two main factors: slow water oxidation kinetics and poor charge separation. We confirm recent reports that cobalt phosphate (Co-Pi) is an efficient water oxidation catalyst for BiVO 4 and report an AM1.5 photocurrent of 1.7 mA/cm 2 at 1.23 V vs RHE for 100 nm spray-deposited, compact, and undoped BiVO 4 films with an optimized Co-Pi film thickness of 30 nm. The charge separation of these films depends strongly on light intensity, ranging from 90% at low light intensities to less than 20% at intensities corresponding to 1 sun. These observations indicate that the charge separation efficiency in BiVO 4 is limited by poor electron transport and not by the presence of bulk defect states, interface traps, or the presence of a Schottky junction at the back-contact.